1. Field of the Invention
The present invention relates to a strengthening device to increase the strength of a grout layer, placed on a concrete base for keeping a structural safety of an upper structure, and more particularly to a strengthening device to increase the strength of a grout layer, which improves a structural safety of an upper structure by fastening the grout layer placed on a concrete base to give a restraining force thereto so that a failure of the grout layer due to loads transferred from the upper structure such as a column member or a bridge bearing installed on the grout layer may be prevented or minimized.
2. Description of the Related Art
As is well known in the art, a grout layer is placed on a concrete base to act for adjusting a vertical position and a horizontal state of an upper structure so that the upper structure such a column member or a bridge bearing may be installed on the concrete base.
In addition, in the case that the upper structure is a column member, the grout layer plays another role of distributing vertical load F (see FIG. 1) and moment load M1 and M2 (see FIG. 1) transferred through a column of the column member.
Thus, such a grout layer should have sufficient strength to resist bearing failure or edge failure.
In the case where the upper structure is a column member for example, the grout layer formed on a concrete base by placing non-shrinkage mortar at a position right below the column of the column member provides a bearing strength sufficiently resisting against a vertical load F (see FIG. 1) and a moment load M1 and M2 (see FIG. 1) transferred down through the column.
However, since an edge of the grout layer has no restraining force applied inward from the outline, the strength of the edge against the moment load is relatively weaker than that against the vertical load.
For example, if a large moment load M1 or M2 (see FIG. 1) is applied to a column member, or an upper structure installed on the grout layer, due to wind or earthquake, a great bearing stress is generated at the edge and corner of a base plate of the column member installed on the grout layer due to rotation of the base plate.
The excessive bearing stress generated along the edge or the corner of the grout layer becomes a fatal factor of crack or failure on the grout layer unless a restraining force is applied inward (or, toward a center) from an outline of the grout layer.
As a result, moment loads repeatedly applied to the upper structure such as a column member may break down the grout layer easily.
In addition, this phenomenon makes it difficult that loads transferred from the upper structure are distributed to the concrete base, resulting in deteriorated structural safety of the grout layer as well as the upper structure such as a column member or a bridge bearing installed thereon.
Accordingly, there has been needed a technique for a strengthening device (or, a reinforcing device) to increase the strength of a grout layer, which may surround and clamp an outline of a grout layer on a concrete base on which an upper structure such as a column member or a bridge bearing is installed so as to improve the safety of the grout layer as well as an upper structure installed thereon, so that the strength of the grout layer, particularly bearing strength at its edge or corner may be enhanced.